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This Article Abstract Full Text (PDF) All Versions of this Article: 90/4/587    most recent expphysiol.2005.030387v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gabbett, T. J Articles by Gass, G. C Search for Related Content PubMed PubMed Citation Articles by Gabbett, T. J Articles by Gass, G. C Related Collections Human, Environmental & Exercise

¹ Athlete and Coach Support Services, Queensland Academy of Sport, Queensland, Australia ² School of Physiotherapy and Exercise Science, Griffith University Gold Coast, Queensland, Australia

	Abstract

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The purpose of this study was to investigate the short-, medium- and long-term reproducibility of cardiovascular responses during 90° head-up tilt (HUT) in healthy older men. Twenty-eight healthy male subjects aged 69 (95% confidence intervals, 68–70) years participated in the study. Eight subjects underwent duplicate 90° HUT tests on consecutive days, while 20 subjects underwent four 90° HUT tests performed at baseline, and after 1 week, 1 month and 1 year. Following a 20-min supine resting period, each subject was rapidly tilted to the upright vertical position (90° HUT) and remained in that position for 15 min. Beat-by-beat recordings of mean (MAP), systolic (SBP) and diastolic (DBP) pressures were made via Finapres, while heart rate (HR) was monitored continuously from an electrocardiogram. No significant test–retest differences (P > 0.05) were observed for the changes in HR, MAP, SBP or DBP during 90° HUT. These measurements demonstrated high reproducibility (intraclass correlation coefficient, r = 0.91–0.99, P < 0.05). The supine resting and tilted HR, MAP, SBP and DBP over the 1-week, 1-month and 1-year period were not significantly different (P > 0.05) from baseline, and demonstrated high reproducibility (intraclass correlation coefficient, r = 0.82–0.98, P < 0.05). The results of this study demonstrate that in healthy older men, cardiovascular responses during orthostasis are highly reproducible, and this reproducibility is maintained over a 12-month period. These findings demonstrate that the 90° HUT test offers a reproducible method of monitoring longitudinal orthostatic responses in healthy older men.

(Received 27 February 2005; accepted after revision 7 April 2005; first published online 15 April 2005)
Corresponding author T. Gabbett: Queensland Academy of Sport, PO Box 956, Sunnybank, Queensland 4109, Australia. Email: tim.gabbett{at}qld.gov.au

	Introduction

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Orthostasis can be generally defined as any environmental process that produces physiological effects similar to those induced by the upright, stationary posture (Convertino, 1987). When humans assume the upright posture, approximately 600 ml blood is displaced from the central circulation into the veins of the legs, buttocks, pelvis and splanchnic circulation (Smith & Ebert, 1990; Rowell, 1993). During events where the muscle pump is inactive, blood pools in the lower extremities, thereby reducing venous return, stroke volume and cardiac output. Under these conditions, the arterial baroreceptors evoke significant increases in heart rate (HR) and total peripheral resistance in an attempt to return arterial pressure (AP) towards a normal homeostatic level (Rowell, 1993).

Orthostatic tests are commonly used in physiological testing laboratories (Smith & Ebert, 1990) and clinical diagnostic facilities (e.g. hospitals), and have recently been used in the diagnosis of athlete overtraining (Uusitalo et al. 1996; Uusitalo et al. 2000; Gabbett et al. 2001a). Additionally, orthostatic testing has been used extensively to assess the age-associated increase in postural hypotension (Maclennan et al. 1980; Lye et al. 1990; Tonkin et al. 1991; Gabbett et al. 2000, 2001b). While orthostatic testing has been used extensively, the reliability of these procedures has been questioned (Lightfoot et al. 1991; Jost et al. 1994; Ward & Kenny, 1996; Herpin & Ragot, 1997). It has been demonstrated that duplicate lower body negative pressure tests produce reliable cardiovascular responses (Lightfoot et al. 1991). In a study of younger (mean age, 33 years), middle-aged (mean age, 54 years), and older (mean age, 76 years) subjects, Patel et al. (1993) reported that asymptomatic postural reductions in systolic blood pressure in response to head-up tilt (HUT) were reproducible 1 week after initial testing. Furthermore, the medium-term (1 week) and long-term (1 year) baroreflex responses have also proven to be reliable (r = 0.54–0.87) in healthy, young adults (Herpin & Ragot, 1997). However, others have suggested that the HR (Giaconi et al. 1987; Jost et al. 1994; Ward & Kenny, 1996) and AP (Giaconi et al. 1987; Jost et al. 1994; Piha, 1991; Ward & Kenny, 1996) responses during HUT are unreliable, and in fact show marked variation across days.

There are conflicting reports regarding the relative cardiovascular responses of young and older subjects to an orthostatic challenge. It has been reported that young and older subjects exhibit similar reductions in stroke volume (Smith et al. 1984), cardiac output (Smith et al. 1984) and AP (Wieling et al. 1992) during active standing and HUT. In contrast, White et al. (1997) and Taylor et al. (1992) demonstrated that older subjects had superior control of AP compared with younger subjects during standing, HUT and lower body negative pressure. In addition, a recent investigation showed that in comparison to older men, young men exhibit larger reductions in AP and a greater reflex overshoot in AP in response to HUT (Gabbett et al. 2001b). On the basis of these equivocal findings, it is possible that the reproducibility of orthostatic responses differs between young and older individuals.

The short- (1 week) (Patel et al. 1993) and medium-term (1 month) (Giaconi et al. 1987; Piha, 1991) reliability of orthostatic responses has been investigated in healthy young (Piha, 1991; Patel et al. 1993) and older (Patel et al. 1993) individuals, and borderline hypertensive (Giaconi et al. 1987) subjects. However, no study has investigated the reliability of orthostatic responses over a prolonged period of time in older individuals. Given that orthostatic tests are commonly used to assess the age-associated increase in postural hypotension (Robinson et al. 1983; Smith & Fasler, 1983; Vargas et al. 1986; Gabbett et al. 2000, 2001b), establishing reliable cardiovascular responses during orthostatic stress is imperative. Therefore, the purpose of this study was to investigate the short, medium and long-term reliability of cardiovascular responses during 90° HUT in healthy men aged between 65 and 75 years. Specifically, this study evaluated the reliability of cardiovascular responses produced by 90° HUT over (a) two consecutive days (Day 1 and Day 2), and over (b) a 1-week, 1-month and 1-year period (Baseline, One Week, One Month and One Year, respectively).

	Methods

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Subjects

Twenty-eight healthy older men (69 (95% confidence intervals, 68–70) year) participated in this study to determine the test–retest reliability of cardiovascular responses during supine rest and 90° HUT. Eight subjects underwent duplicate 90° head-up tilt (HUT) tests on consecutive days (Day 1 versus Day 2), while 20 subjects underwent four tests performed at baseline, 1 week (short term), 1 month (medium term), and 1 year (long term) apart (Baseline, One Week, One Month, One Year, respectively). Subjects were non-smokers with normal pulmonary function, resting 12-lead electrocardiogram and echocardiogram, and supine resting AP of less than 160/90 mmHg. Each subject completed a comprehensive medical examination and an incremental exercise test to volitional exhaustion without any clinically significant findings (Table 1). Subjects were not prescribed or taking and medication that was likely to interfere with cardiovascular responses. All subjects received a clear explanation of the study, including the risks and benefits of participation, and written consent was obtained. All experimental procedures were approved by the Griffith University Ethics Committee for Human Experimentation.

Prior to conducting the reliability study each subject was familiarized with the tilt table. Familiarization sessions were identical for all subjects. All tests were conducted in a temperature-controlled environment (22–24°C, dry bulb). Subjects were encouraged to void their bladder immediately before the commencement of the test. The subjects lay supine and electrocardiographic (ECG) electrodes were applied in the CM5 position. Beat-by-beat measurements of HR were obtained from an electrocardiograph (Lohmeier M607, Munchen, Germany) while continuous systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were obtained non-invasively via Finapres (Ohmeda 2300, Louisville, CO, USA) which was applied to the middle finger of the subject's left hand. Pulse pressure (PP) was calculated from the difference between SBP and DBP. The Finapres device was maintained by supportive strapping at heart level throughout the entire experimental procedure. Three 10-cm wide adjustable straps secured the subjects to the table. The straps were firmly, but comfortably applied around the chest, thigh and calves of the participants. The amplified signals from the Finapres and electrocardiograph were collected at 100 Hz using a Biopac system (MP 100, SDR Clinical Technology, Middle Cove, Australia) and Acqknowledge 2.0 software package. Subjects were requested to remain relaxed, maintain normal respiration, and avoid all muscle contraction. The lights in the room were dimmed and subjects were instructed to close their eyes to promote relaxation.

All subjects rested in the supine position for 20 min. To minimize anticipatory changes in HR or AP, each subject was randomly assigned an additional rest period ranging from 2 to 10 min prior to 90° HUT. At the completion of the additional randomized 2- to 10-min rest period, subjects were tilted smoothly and rapidly to the 90° HUT position within 2 s. During 90° HUT, the subject was supported by a cushioned footplate. Beat-by-beat HR and AP values were recorded continuously during 90° HUT for a period of 15 min. No conversation was made between the subject and investigators throughout the 90° HUT experiment. Finger AP was recorded at 1-min intervals throughout supine rest and 15 min of 90° HUT.

Statistics

The normality of data was confirmed using a Shapiro-Wilk test. Changes in HR, SBP, DBP and MAP from supine rest were analysed using an analysis of variance (ANOVA) with repeated measures design. Differences among the various test conditions were evaluated using paired t tests (Day 1 versus Day 2), and ANOVA with repeated measures (Baseline versus One Week versus One Month versus One Year). Test–retest reliability was evaluated using intraclass correlation coefficient (ICC) (Shrout & Fleiss, 1979) and the typical error of measurement (TEM). Data are reported as mean and 95% confidence interval (CI).

	Results

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Reliability of orthostatic responses: Day 1 versus Day 2

No significant differences (P > 0.05) existed between Day 1 and Day 2 for supine resting SBP, DBP and HR prior to 90° HUT (Table 2). In addition, the HR, MAP, SBP and DBP following 15 min of 90° HUT were not significantly different (P > 0.05) between Day 1 and Day 2 and also proved to be reliable (ICC, r = 0.91–0.99, P < 0.05). A weak, insignificant relationship (ICC, r = 0.66, P > 0.05) was observed between Day 1 and Day 2 for PP at supine rest.

No significant differences (P > 0.05) existed between Baseline, One Week, One Month and One Year for supine resting SBP, DBP and HR prior to 90° HUT. In addition, the HR, SBP, DBP and MAP during 90° HUT were not significantly different (P > 0.05) over the 1-week, 1-month and 1-year period. These measurements demonstrated high reliability (ICC, r = 0.82–0.98, P < 0.05) (Table 3). An example of HR and MAP responses during supine rest and 90° HUT in one older subject is shown in Fig. 1.

View larger version (21K): [in this window] [in a new window]   Figure 1.  Reliability of heart rate and mean arterial pressure responses Short- (1 week), medium- (1 month) and long-term (1 year) reliability of heart rate (dotted line) and mean arterial pressure (solid line) responses at supine rest and during 15 min of 90° head-up tilt (HUT) in one healthy older subject.

	Discussion

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In the present study, we found that duplicate measurements of supine resting and orthostatic HR, SBP, DBP and MAP were reliable in healthy older men. These findings are in agreement with Lightfoot et al. (1991), who found that duplicate lower body negative pressure tests produce reliable cardiovascular responses in young individuals. In addition, these findings are in agreement with Patel et al. (1993) who reported that asymptomatic postural reductions in systolic blood pressure in response to HUT were reproducible 1 week after initial testing in younger, middle-aged and older individuals. However, these results are in conflict with others, who have suggested that the HR (Giaconi et al. 1987; Jost et al. 1994) and AP (Giaconi et al. 1987; Piha, 1991; Ward & Kenny, 1996) responses during HUT are unreliable, and show marked variation across days. The discrepant findings of the present and previous studies (Ward & Kenny, 1996) are most probably explained by differences in the subject population. The present study investigated healthy older men while the subjects in the study of Ward & Kenny (1996) were symptomatic older patients with neural disorders and/or ischaemic cardiovascular disease. While the results of Ward & Kenny (1996) may suggest that AP responses may be unreliable in symptomatic older individuals, the results of the present study demonstrate that under the present experimental conditions, HR, SBP, DBP and MAP responses at supine rest and during 90° HUT are highly reliable in healthy older men.

In the present study, HR responses at supine rest and during 90° HUT demonstrated good short- (1 week), medium- (1 month) and long-term (1 year) reliability. The SBP, DBP and MAP, measured by Finapres, were also reliable over the short, medium and long term. These findings confirm, and extend those of others (Patel et al. 1993) who found that short-term (1 week) SBP responses in response to HUT were reproducible in healthy subjects. Furthermore, the ICC over the 1-year period (r = 0.82–0.98) in the healthy older subjects of the present study were comparable to the baroreflex response reliability data (r = 0.54–0.87) reported in healthy young adults (Herpin & Ragot, 1997). Given the reliability of HR, SBP, DBP and MAP measurements, these results suggest that the 90° HUT test in combination with Finapres can be reliably used to assess orthostatic responses in healthy older men. In addition, these results confirm the findings of Herpin & Ragot (1997) by demonstrating sufficient reliability of orthostatic responses to allow studies to be conducted over a short, medium or long period.

In the present study we found that test–retest measurements of PP during supine rest and 90° HUT were moderately correlated (r = 0.59–0.91). As PP is calculated from the difference between SBP and DBP, the modest reliability of PP most probably reflects the combined variability of SBP and DBP measurements. Significant reductions in AP and PP, coupled with increases in HR, have been suggested as evidence of arterial baroreceptor activation (Zoller et al. 1972). While acknowledging the physiological significance of changes in PP in determining baroreflex activation and orthostatic responses, in terms of reliability, the present results demonstrate that MAP is a more reliable method of assessing orthostatic responses and baroreflex function in healthy older men. In addition, given the significant correlation between quadruplicate tests for PP, these results suggest that if PP is of clinical importance, multiple orthostatic tests should be used and scores averaged in order to reliably determine the PP of an individual during orthostasis.

In summary, the results of this study demonstrate that in healthy older men, cardiovascular responses during orthostasis are highly reliable, and this reliability is maintained over a 12-month period. These findings demonstrate that the 90° HUT test offers a reproducible method of monitoring longitudinal orthostatic responses in healthy older men.

	References

Top Abstract Introduction Methods Results Discussion References

 
Convertino VA (1987). Aerobic fitness, endurance training, and orthostatic intolerance. Exerc Sports Sci Rev 15, 223–259.

Gabbett T, Gass G, Gass E, Morris N, Bennett G & Thalib L (2000). Norepinephrine and epinephrine responses during orthostatic intolerance in healthy elderly men. Jpn J Physiol 50, 59–66.[CrossRef][Medline]

Gabbett TJ, Gass GC, Thalib L, Morris N & Gass EM (2001a). Does endurance training affect orthostatic responses in healthy elderly men? Med Sci Sports Exerc 33, 1279–1286.[CrossRef][Medline]

Gabbett TJ, Weston SB, Barrett RS & Gass GC (2001b). Cardiovascular regulation during head-up tilt in healthy 20–30-year-old and 70–75-year-old men. Clin Sci 100, 199–206.[Medline]

Giaconi S, Palombo C, Genovesi-Ebert A, Marabotti C, Mezzasalma L & Ghione S (1987). Medium-term reproducibility of stress tests in borderline arterial hypertension. J Clin Hypertens 3, 654–660.[Medline]

Herpin D & Ragot S (1997). Mid- and long-term reproducibility of noninvasive measurements of spontaneous arterial baroreflex sensitivity in healthy volunteers. Am J Hypertens 10, 790–797.[CrossRef][Medline]

Jost WH, Rapp C, Konig J & Schimrigk K (1994). Are heart rate responses reproducible in the tilt-table test? Clin Invest 72, 996–999.[CrossRef][Medline]

Lightfoot JT, Hilton F & Fortney SM (1991). Repeatability and protocol comparability of presyncopal symptom limited lower body negative pressure exposures. Aviat Space Environ Med 62, 19–25.[Medline]

Lye M, Vargas E, Faragher EB, Davies I & Goddard C (1990). Haemodynamic and neurohumoral responses in elderly patients with postural hypotension. Eur J Clin Invest 20, 90–96.[Medline]

Maclennan WJ, Hall MRP & Timothy JI (1980). Postural hypotension in old age: is it a disorder of the nervous system or of blood vessels? Age Ageing 9, 25–32.[Abstract/Free Full Text]

Patel A, Maloney A & Damato AN (1993). On the frequency and reproducibility of orthostatic blood pressure changes in healthy community-dwelling elderly during 60-degree head-up tilt. Am Heart J 126, 184–188.[Medline]

Piha SJ (1991). Cardiovascular autonomic reflex tests: normal responses and age-related reference values. Clin Physiol 11, 277–290.[Medline]

Robinson BJ, Johnson RH, Lambie DG & Palmer KT (1983). Do elderly patients with an excessive fall in blood pressure on standing have evidence of autonomic failure? Clin Sci 64, 587–591.[Medline]

Rowell LB (1993). Human Cardiovascular Control. Oxford University Press, New York.

Shrout PE & Fleiss JL (1979). Intraclass correlations: uses in assessing rater reliability. Psychol Bull 86, 420–428.[CrossRef][Medline]

Smith JJ, Barney JA, Porth CJ, Groban L, Stadnicka A & Ebert TJ (1984). Transient hemodynamic responses to circulatory stress in normal male subjects of different ages. Physiologist 27, 210.

Smith JJ & Ebert TJ (1990). General response to orthostatic stress. In Circulatory Response to the Upright Posture, ed. Smith JJ, pp. 1–46. CRC Press, Boca Raton, Florida.

Smith SA & Fasler JJ (1983). Age-related changes in autonomic function: relationship with postural hypotension. Age Ageing 12, 206–210.[Abstract/Free Full Text]

Taylor JA, Hand GA, Johnson DG & Seals DR (1992). Sympathoadrenal–circulatory regulation of arterial pressure during orthostatic stress in young and older men. Am J Physiol 263, R1147–R1155.

Tonkin AL, Wing LMH, Morris MJ & Kapoor V (1991). Afferent baroreflex dysfunction and age-related orthostatic hypotension. Clin Sci 81, 531–538.[Medline]

Uusitalo ALT, Tahvanainen KUO, Uusitalo AJ & Rusko HK (1996). Non-invasive evaluation of sympathovagal balance in athletes by time and frequency domain analyses of heart rate and blood pressure variability. Clin Physiol 16, 575–588.[Medline]

Uusitalo ALT, Uusitalo AJ & Rusko HK (2000). Heart rate and blood pressure variability during heavy training and overtraining in the female athlete. Int J Sports Med 21, 45–53.[CrossRef][Medline]

Vargas E, Lye M, Faragher EB, Goddard C, Moser B & Davies I (1986). Cardiovascular haemodynamics and the response of vasopressin, aldosterone, plasma renin activity and plasma catecholamines to head-up tilt in young and old healthy subjects. Age Ageing 15, 17–28.[Abstract/Free Full Text]

Ward C & Kenny RA (1996). Reproducibility of orthostatic hypotension in symptomatic elderly. Am J Med 100, 418–422.[CrossRef][Medline]

White M, Courtemanche M, Stewart DJ, Talajic M, Mikes E, Cernacek P, Vantrimpont P, Leclerc D, Bussieres L & Rouleau JL (1997). Age- and gender-related changes in endothelin and catecholamine release, and in autonomic balance in response to head-up tilt. Clin Sci 93, 309–316.[Medline]

Wieling W, Veerman DP, Dambrink JHA & Imholz BPM (1992). Disparities in circulatory adjustment to standing between young and elderly subjects explained by pulse contour analysis. Clin Sci 83, 149–155.[Medline]

Zoller RP, Mark AL, Abboud FM, Schmid PG & Heistad DD (1972). The role of low pressure baroreceptors in reflex vasoconstrictor responses in man. J Clin Invest 51, 2967–2972.

This Article Abstract Full Text (PDF) All Versions of this Article: 90/4/587    most recent expphysiol.2005.030387v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gabbett, T. J Articles by Gass, G. C Search for Related Content PubMed PubMed Citation Articles by Gabbett, T. J Articles by Gass, G. C Related Collections Human, Environmental & Exercise